The present invention relates to a cigarette manufacturing method providing for short tobacco distribution control. On cigarette manufacturing machines, cigarettes are known to be made starting from a continuous rod produced by folding a continuous strip of paper crosswise round a stream of shredded tobacco fed continuously on to the said strip of paper.
The physical characteristics of the cigarettes produced by cutting the said continuous rod crosswise are invariably inconsistent, at times varying considerably from one cigarette to another.
The cigarettes coming off the same machine and made from the same batch of tobacco invariably differ in weight, permeability and the extent to which the tobacco is held inside. Such differences are caused by the non-homogeneous nature of the tobacco and, consequently, of the stream of tobacco produced and deposited on to the said continuous strip of paper, the reason for this being uneven distribution of the different-size particles of which the tobacco is composed.
Shredded tobacco, in fact, is known to comprise relatively long strips, generally referred to as "long tobacco", and shorter strips, generally referred to as "short tobacco" and which usually also include tobacco dust.
The percentage of long or short tobacco not only varies from one batch of tobacco to another of the same quality, but also over time within the same batch, depending on the amount of handling the tobacco is subjected to.
Furthermore, the short tobacco in the mass is never evenly distributed, tending as it does to gravitate down through the thinner long tobacco and collect at the bottom.
Owing to poor blending of the long and short tobacco in the overall mass, the tobacco supply to the input feedbox on cigarette manufacturing machines usually results in a stream of tobacco in which the percentages of long and short tobacco vary in purely random "waves".
The inevitable drawback of such a situation is that the cigarettes coming off the machine differ as to physical characteristics, i.e. one cigarette may be produced containing a high percentage of long tobacco and, therefore, highly permeable and lightweight, whereas the next may contain a high percentage of short tobacco resulting in heavy weight, low permeability and poor hold, owing to the tendency of short tobacco to leak out if not held together by long tobacco.
In an attempt to overcome these drawbacks, cigarette manufacturing machines are known to be fitted with devices for regulating the distribution of short tobacco within the mass of tobacco being fed to the machine output.
Such a regulating device is described in British Pat. No. 1.101.071 which relates to a cigarette manufacturing machine on which, at a given point on the route travelled by the tobacco moving through the machine, the short tobacco is separated from the long tobacco and fed to a tank from which it is drawn off and fed to another point on the said tobacco route downstream from the said withdrawal point.
According to one feature of this machine, the stream of short tobacco coming out of the storage tank is regulated in such a manner as to be directly proportional to the amount of short tobacco collected inside the tank.
In this way, for example, if the machine is fed with a given quantity of predominantly short tobacco, the latter is drawn off from the mass of tobacco moving through the machine, with the result that a stream of essentially long tobacco is formed on the machine downstream from the said withdrawal point.
Subsequently, short tobacco is blended into the long-tobacco stream, the amount of short tobacco being proportional to the amount of the same collected in the storage tank. Consequently, the abovementioned known type of machine successfully provides for preventing the production of faulty cigarettes consisting essentially of short tobacco, by eliminating short-tobacco supply "peaks", which are redistributed by mixing short tobacco into the long-tobacco stream.
Though the abovementioned machine succeeds in preventing the production of faulty cigarettes consisting essentially of short tobacco, it should be pointed out that it definitely does not succeed in reducing the said differences in weight and permeability below a given level.
While, on the one hand, the abovementioned machine succeeds in ironing out the short-tobacco supply peaks, on the other, it most certainly does not succeed, for example, in making up for a shortage of such tobacco, should the machine be fed with a given quantity of predominantly long tobacco. In the event of this happening, the rate at which short tobacco is collected inside and fed out of the storage tank is essentially zero.
Consequently, for a given length of time, the cigarettes coming off the machine will consist mainly of long tobacco, the weight and permeability of which may differ to an unacceptable degree from cigarettes of the same type containing an appreciable percentage of short tobacco.